RE: Effect of increasing plenum size?

Tuned length runners will by design favor one or possibly more than one narrow rpm bands at the expense of causing torque "valleys" elsewhere. If your goal is peak HP, the length can be tailored to promote this, based on the expected peak HP rpm. If you want a broad, flat torque curve, you're better off with very short runners and a decent sized plenum.The trade-off of increasing plenum size is slower throttle response.Depending on the means at your disposal you can either experiment with hardware, or model the engine in software, and iterate to find the solution you are seeking.

RE: Effect of increasing plenum size?

Yes I am aware of runner length and diameter tuning, but as mentioned above due to packaging there isn't anything I can do to that.

To simplify it, basically I just want to know if enlarging the plenum sizes alone will have a positive benefit. I am OK with slower throttle response and possibly a TQ loss at one RPM as a trade off for a gain elsewhere..

RE: Effect of increasing plenum size?

Actually you can change the runner length and diameter usually on your setup if you are willing to go through the work involved. With your current setup and the fact that you don't feel you picked anything with the porting, you should probably look at the camshaft at this time. Increasing runner volume is just going to move the power band higher in the rpm scale. What kind of engine are we talking about here? With the dual runner lengths, it sounds like you could be working on a SHO Taurus. The different runner lengths should be controlled by vacuum on your setup depending on your throttle position.

Larry

RE: Effect of increasing plenum size?

the first thing to do is check that the manifold is passing on the air flow to the head, we have done a fare amount on airflow work on plastic intake/plenum and found as much as20% restiction to flow so it may pay to test yours before you get to plenum volume.or make any radical change

RE: Effect of increasing plenum size?

bigpaul is right on his statement. That is why you should always test the actual parts you are going to be using when flow testing the cylinder head. It is not unusual for airflow to drop by 20 to 50cfm when you test a head with the intake manifold attached vs. a radiused flow entry plate.

RE: Effect of increasing plenum size?

A bigger plenum goes hand and hand with shorter runners/higher RPMs for one thing. However, because most stock manifolds are not even close to being fluidynamically matched to the valve flowing into the cylinder you will almost always have manifold flow restrictions. Even upon the application of a flow radius. As long as the short sides and long sides of the port are unequal in length at the entry of the runner you will not get any closer to the best possible results.